A large fraction of the electricity use in the United States is associated with lighting. LED lighting sources have huge advantages over conventional sources in terms of cost of use and impact on energy production, but high fabrication cost and limited brightness have limited adoption of solid state lighting outside certain niche applications such as traffic lights.
Sapphire is most commonly used as the substrate for nitride light emitting diodes (LEDs) in solid state lighting due to its physical robustness and high-temperature stability. A low-dislocation density GaN semiconductor template on sapphire is important for high-efficiency and reliable nitride light-emitting diodes (LEDs) in solid state lighting applications. In conventional metalorganic vapor phase epitaxy (MOVPE) of GaN on a sapphire substrate, the low temperature GaN buffer layer is etched-back by employing H2 at high temperature to form micron-sized GaN islands. The use of intentional delay of the nucleation island coalescence (recovery) reduces threading dislocation density. The etch-back and recovery process employed in conventional MOVPE of GaN on sapphire substrate adds 30 to 45 minutes in the GaN growth time, which increases the cost of epitaxy process.
The threading dislocation density of conventional MOVPE grown GaN template is still relatively high in the range of 108-1010 cm−2. Several techniques have been utilized to reduce the threading dislocation density in MOVPE grown GaN template, such as lateral epitaxial overgrowth (LEO), pendeo epitaxy, and cantilever epitaxy. These approaches have led to reduction in the dislocation density of GaN template down to 106-107 cm−2, however the high quality material is limited in the narrow 2-3 μm stripe regions.